Distributed power railroad train operation supplies motive power and braking action from a lead locomotive (or lead unit) and one or more remote locomotives (or remote units) spaced apart from the lead unit in a train. In one configuration, a distributed power train comprises a lead locomotive at a head end of the train, a remote locomotive at an end of train (EOT) position and one or more mid-train locomotives disposed between the head end and the end of train. Distributed train operation may be preferable for long train consists to improve train handling and performance.
In a distributed power train, each lead and remote locomotive supplies motive power and braking action for the train. Motive and braking command messages are issued by an operator in the lead locomotive and supplied to the remote locomotives over a radio frequency communications system, (such as the prior art LOCOTROL® distributed power communications system, available from the General Electric Company of Schenectady, N.Y.) comprising a radio frequency link and receiving and transmitting equipment at the lead and the remote units. The receiving remote locomotives respond to these commands to apply tractive effort or braking effort to the train, and advise the lead unit of the receipt and execution of the received command. The lead unit also sends other messages to the remote units, including status request messages. The remote units respond by sending a status reply message back to the lead unit.
In a train where two or more locomotives are coupled together and thus function in unison via signals transmitted over their connected MU (multiple unit) lines, one of the locomotives is designated as a controlling remote unit with respect to the distributed power communications system. Only the controlling remote unit is configured to receive commands transmitted by the lead unit and respond to the lead unit with appropriate reply messages.
One of the most critical aspects of train operation is the predictable and successful operation of the air brake system. The air brake system comprises locomotive brakes in each locomotive (including the lead locomotive and all the remote locomotives) and car brakes at each railcar. The lead unit locomotive brakes are controlled by the locomotive operator in response to a position of a locomotive brake handle, and the rail car brakes are controlled in response to a position of an automatic brake handle. The locomotive brakes can also be controlled by the automatic brake handle.
The automatic brake controller controls a pressure in a fluid carrying brake pipe that extends the length of the train and is in fluid communication with a car brake system for applying or releasing car brakes at each railcar in response to a pressure change in the brake pipe. Specifically, a control valve (typically comprising a plurality of valves and interconnecting piping) at each railcar responds to changes in the brake pipe fluid pressure by applying the brakes (in response to a decrease in the brake pipe fluid pressure) or by releasing the brakes (in response to an increase in the brake pipe fluid pressure). The fluid within the brake pipe conventionally comprises pressurized air. In a conventional train having only a consist of locomotives at the head end, operator control of the automatic brake handle in the lead locomotive initiates a pressure drop that propagates along the brake pipe toward the end of the train. The control valve at each railcar senses the pressure drop and in response thereto supplies pressurized air from a local railcar reservoir to wheel brake cylinders that in turn draw brake shoes against railcar wheels. The railcar reservoir is recharged by air withdrawn from the brake pipe during non-braking operational intervals. A brake release is also commanded by the lead operator by controlling the automatic brake handle to effect a pressure increase in the brake pipe. The pressure increase is sensed at the railcars, and in response, the brake shoes are released from the railcar wheels. With some limitations as required to maintain train control, in a distributed power train, a brake command or brake release can be commanded by the lead or the remote locomotives.
The railcar brakes can be applied in two modes, i.e., a service brake application or an emergency brake application. In a service brake application, braking forces are applied to the railcar to slow or bring the train to a stop at a forward location along the track. During service brake applications the brake pipe pressure is slowly reduced and the brakes are applied gradually in response thereto. The operator controls the rate at which the pressure is reduced by operation of the automatic brake control handle. A penalty brake application is a service brake application in which the brake pipe is reduced to zero pressure, but the evacuation occurs at a predetermined rate, unlike an emergency brake application as described below and the railcars do not vent the brake pipe.
An emergency brake application commands an immediate application of the railcar brakes through an immediate evacuation or venting of the brake pipe. When a railcar senses a predetermined pressure reduction rate, indicative of an emergency brake application, the railcar also vents the brake pipe to accelerate propagation of the brake pipe evacuation along the train. Unfortunately, because the brake pipe runs for several thousand yards through the train, the emergency brake application does not occur instantaneously along the entire length of the brake pipe. Thus the braking forces are not uniformly applied at each railcar to stop the train.
On distributed power trains, braking is accomplished by venting the brake pipe at both the lead and remote locomotives, thus accelerating the brake pipe venting and application of the brakes at each railcar, especially for those railcars near the end of the train. As can be appreciated, brake pipe venting at only the lead unit in a conventional train requires propagation of the brake pipe pressure reduction along the length of the train, thus slowing brake applications at railcars distant from the lead unit. For a distributed power train with an operative communications link between the lead and remote units, when the train operator commands a brake application (e.g., a service or an emergency brake application) by operation of the automatic brake control handle at the lead unit, the brake pipe is vented and a brake application command is transmitted to each remote unit over the radio frequency communications link. In response, each remote unit also vents the brake pipe. Thus braking action at the remote locomotives follows the braking action of the lead unit in response to signals transmitted by the communications system.
A brake release initiated at the lead unit is also communicated over the radio frequency link to the remote units so that the brake pipe is recharged from all locomotives, reducing the brake pipe recharge time.
If an emergency brake application is initiated at the lead locomotive by the train operator or due to a detected failure condition, the radio frequency communication system sends an emergency brake signal to each of the remote locomotives over the radio frequency link. In response, the remote locomotives evacuate the brake pipe. This permits faster execution of the emergency brake application since the brake pipe is being evacuated from all of the locomotives, rather than from only the lead locomotive as in a conventional train.
During certain railroad operations, it is desirable to swap or reverse the operational status of the remote and lead units such that the lead unit at the head of the train is reconfigured as a remote unit at the end of the train, and the remote unit at the end of the train is reconfigured as the lead unit. For example, when unloading a coal train at an electrical generating plant track spur, the train passes through the dumping area in one direction until each railcar has dumped a coal load. The train is then reversed to exit the spur in a reverse direction, i.e., the lead locomotive pushes the train in reverse to exit the spur. If the train comprises a distributed power train, it would be desirable to swap the lead and the end-of-train remote unit's functionality to avoid operating both these units in reverse. The train could then be driven from the spur track with the head end unit operating in a forward direction such that the train is pulled along the track, rather than pushing the train from the end-of-train. A similar situation arises when a distributed power train enters a mine spur where the railcars are loaded with material extracted from the mine. The LOCOTROL® communication system includes a feature that permits each locomotive in the train to operate as a lead unit or as a remote unit, although the unit must be reconfigured or reprogrammed to change its operational status.
As can be appreciated by those skilled in the art, there are other operating scenarios to which the teachings of the present invention can be applied. For example, it is desired to switch a distributed power train traveling west on an east-west track to travel north on a north-south intersecting track. Assuming the north-south track has only a south bound entry from the east-west track, the train switches to the south bound leg of the north-south track such that the lead locomotive enters the south bound leg first and an end-of-train locomotive enters the south bound leg last. After the entire train has entered the southbound leg, the track switch is operated to align the southbound leg with the northbound leg. To proceed north, the lead unit, now at the end of the train, is operated in reverse. The end of train unit also operates in reverse and leads the train out of the southbound leg onto the northbound leg. Here too it would be preferable to swap the lead and the remote locomotive functionalities so that both are operating in a forward direction and the locomotive at the head of the train is the lead locomotive with respect to the distributed power communications system.
It is not a trivial matter to reverse a distributed power train that employs a communication system for transmitting signals between the lead unit and the remote units. Each remote unit requires lead unit identification information to process and respond to received messages, and each remote unit is configured to respond to commands and messages from only that lead unit. Thus when the lead unit is changed, each of the remote units must be reconfigured to accept commands and messages from the new lead unit, i.e., identification information for the new lead unit must be supplied to each of the remote locomotives. Also, the former lead unit must be reconfigured to remote unit functionality. The operating direction (also referred to as train line orientation) of certain of the locomotives must also be reversed.
In a distributed power train having a locomotive at the rear end of the train, it is common practice for the train crew to perform the following steps to “reverse” the train, thereby permitting operation from a new lead unit that was formerly the end-of-train remote unit.
The lead unit is unlinked from all of the remote units, i.e., the lead unit is reconfigured such that it cannot transmit signals to the remote units, and the remote units are reconfigured such that they cannot receive signals from the lead unit. For safety reasons, when these communication links are terminated, an emergency or a penalty brake application is automatically effectuated to prevent train movement. Both an emergency and a penalty brake application deplete nearly all the air in the brake pipe and a significant volume of air from the railcar reservoirs.
After unlinking the train, the former lead unit is reconfigured to operate as an additional remote unit for receiving commands and messages from a new lead unit. The reconfiguration process includes advising the new remote unit of a unique identifier associated with the new lead unit, e.g., a locomotive road number. All remote units use the lead identification information to confirm that received messages or commands were transmitted from the lead locomotive. Without this confirmation feature, a remote locomotive could respond to a command or message transmitted from a lead unit of another train in the area. The reconfiguration process also includes reversing the operational direction of the former lead unit. That is, if the locomotive was operating in the forward direction, it is configured to operate in the reverse direction. However, during operation the remote unit can be commanded to operate in the forward direction whenever desired, but the unit must be properly configured relative to the operating direction of the lead unit so that commands issued by the lead unit are properly interpreted at the remote unit.
After completing the reconfiguring process to operate the former lead unit as a remote unit, the crew relocates to the new lead unit of the train.
If the distributed power train includes mid-train remote units, these must also be manually reconfigured to permit linking to the new lead unit. Typically, this is accomplished by the crew as they walk from the former lead unit to the new lead unit. Mid-train remote reconfiguration includes supplying each mid-train remote unit with identification information for the new lead unit. For example, a road number for the new lead unit can be used as the identification information. Additionally, the reconfiguration process requires reversing the operational direction of each mid-train remote unit. That is, if a remote unit were previously configured to operate in a forward mode when the former lead unit was operating in the forward direction, the remote unit is reconfigured to operate in a reverse mode when the new lead unit operates in forward. Simply stated, each mid-train remote unit must be configured to operate in either the forward mode or the reverse mode when the lead unit operates in the forward direction, so that forward and reverse commands issued by the lead unit are properly interpreted at the mid-train remote units.
When the crew arrives at the new lead unit, they reconfigure the former remote unit to operate as the new lead unit. This process includes changing the operating direction of the new lead unit and executing a train linking operation to link the lead and remote locomotives to the communications system.
The linking process configures the communications system over which the lead and remote units (including the new remote unit that previously operated as the lead unit) communicate commands and messages. The linking process begins by advising the lead unit of the remote unit road numbers, and creating and sending a link message, in accordance with a predetermined format, from the new lead unit successively to each remote unit. Upon receipt of the message, each remote unit determines whether certain unique address/identification fields in the message match address/identification information of the receiving remote unit and address/identification fields of the sending lead unit. This address/identification comparison process ensures that the received message was intended for the receiving remote unit and was transmitted by the lead unit of the train. If the address/identification information is not in agreement, the remote unit remains in an unlinked condition, i.e., no messages or commands can be exchanged between the lead unit and the unlinked remote unit during train operation.
If the compared address/identification fields agree, the remote unit starts a link timer, and creates and transmits a link reply message having a predetermined format and including address/identification information of the transmitting remote unit. The lead unit receives the link reply message and compares the address/identification fields in the message with stored values to confirm that the message was intended for the receiving lead unit and was transmitted from the appropriate remote unit. If the comparison process does not result in matching address/identification information, the lead unit and the remote unit are not linked.
If the address/identification fields in the link reply message agree, the lead unit transmits a command message to the remote unit that sent the link reply message. At the receiving remote unit, the command completes the link-up sequence and places the remote unit in the linked state. Thereafter messages can be sent and received between the lead unit and the linked remote unit. The process continues until all of the remote units in the train are linked to the lead unit. Once the locomotives are linked, all remote units can recognize commands and messages received from the lead unit to which they are linked, and the lead unit can recognize messages received from remote units to which it is linked.
After the train is linked the emergency or penalty brake application that was commanded at the beginning of the swapping process is released by charging the brake pipe to its nominal pressure value (i.e., about 90 psi in one embodiment). After executing a brake pipe test, to be described below, the communication system is placed in a run mode and the crew in the new lead unit can apply motive power to move the train.
Typically, this prior art process of swapping the lead and remote units incurs a 20 to 60-minute delay penalty before the train can depart. The extent of actual delays varies depending upon train length (which affects brake pipe recharge time), leakage along the brake pipe (requiring a longer period for the brake pipe to fill from the evacuated state due to emergency or penalty brake application), ambient temperature and the number of remote units in the train.
FIGS. 1 and 2 schematically illustrate a distributed power communications system 10 for controlling one or more remote units 12A-12C from either a lead unit 14 (FIG. 1) or a control tower 16 (FIG. 2) in a distributed power train. The teachings of the present invention can be applied to the distributed power communications system 10. In one embodiment, a communications channel of the communications system 10 comprises a single half-duplex communications channel having a three kHz bandwidth, where the messages and commands comprise a serial binary data stream encoded using frequency shift keying modulation. The various bit positions convey information regarding the type of transmission (e.g., message, command, alarm), the substantive message, command or alarm, the address of the receiving unit, the address of the sending unit, conventional start and stop bits and error detection/correction bits. The details of the messages and commands provided by the system and the transmission format of individual messages and commands are discussed in detail in commonly owned U.S. Pat. No. 4,582,280, which is hereby incorporated by reference.
It should be understood that the only difference between the systems of FIGS. 1 and 2 is that the issuance of commands and messages from the lead unit 14 of FIG. 1 is replaced by the control tower 16 of FIG. 2 and certain interlocks of the system of FIG. 1 are eliminated. Typically, the control tower 16 communicates with the lead unit 14, which in turn is linked to the remote units 12A-12C.
A train 18 of FIGS. 1 and 2, further comprises a plurality of railcars 20 interposed between the remote units 12A and 12B and between the remote units 12B and 12C (of FIG. 1). The arrangement of locomotives and cars illustrated in FIGS. 1 and 2 is merely exemplary, as the present invention can be applied to other locomotive/railcar arrangements. The cars 20 are provided with an air brake system (not shown in FIGS. 1 and 2) that applies the railcar air brakes in response to a pressure drop in a brake pipe 22, and releases the air brakes upon a pressure rise in the brake pipe 22. The brake pipe 22 runs the length of the train for conveying the air pressure changes specified by the individual air brake controls 24 in the lead unit 14 and the remote units 12A, 12B and 12C.
An off board repeater 26 may be disposed within radio communication distance of the train 18 for relaying communications signals between the lead unit 14 and one of the remote units 12A, 12B and 12C. The off board repeater 26 is typically installed in a location where direct communications between the lead unit 14 and the remote units 12A-12C is hampered, such as while the train 18 is passing through a tunnel.
The lead unit 14, the remote units 12A, 12B and 12C, the off board repeater 26 and the control tower 16 are provided with a transceiver 28 operative with an antenna 29 for receiving and transmitting communications signals over the communications channel.
The lead unit transceiver 28 is associated with a lead station 30 for generating and issuing commands and messages from the lead unit 14 to the remote units 12A-12C. Commands are generated in lead station 30 in response to operator control of the motive power and braking controls within the lead unit 14, as described above. Each remote unit 12A-12C and the off board repeater 26 comprises a remote station 32 for processing and responding to transmissions from the lead unit 14 and for issuing reply messages and commands.
The four primary types of radio transmissions carried by the communications system include: (1) link messages from the lead unit 14 to each of the remote units 12A-12C that establish the communications system between the lead unit 14 and the remote units 12A-12C, (2) link reply messages that indicate reception and execution of the link message, (3) commands from the lead unit 14 that control one or more functions (e.g., application of motive power or braking) of one or more remote units 12A-12C and (4) status and alarm messages transmitted by the one or more remote units 12A-12C that update or provide the lead unit 14 with necessary operating information concerning the one or more remote units 12A-12C.
Each message and command sent from the lead unit 14 is broadcast to all of the remote units 12A-12C and includes the lead unit identifier. Messages and alarms sent from one of the remote units 12A-12C include the sending unit's address. As a result of the previously completed link-up process, the receiving unit, i.e., the lead or a remote locomotive, can determine whether it was an intended recipient of the received transmission, based upon the sending unit identification included within the message, and can respond accordingly. These four message types, including the address information included in each, ensure a secure transmission link that has a low probability of disruption from interfering signals within radio transmission distance of the train 18, provides control of the remote units 12A-12C from the lead unit 14 and provides remote unit operating information to the lead unit 14.
Although most commands are issued by the lead unit and transmitted to the remote units for execution as described above, there is one situation where a remote issues commands to the other remote units and the lead unit. If a remote unit detects a condition that warrants an emergency brake application, the remote transmits an emergency brake command to all other units of the train. The command includes identification of the lead locomotive of the train and will therefore be executed at each remote unit, as if the command had been issued by the lead unit.
The distributed power communications systems operates in one of two modes, synchronous control and independent control. In synchronous control, the remote units follow the throttle position of the lead unit. If the operator moves the throttle handle from a notch five position to a notch seven position, the communications system commands each of the enabled remote units to operate at a notch seven throttle. If the operator moves the throttle handle to a dynamic brake position (i.e., where the traction motors are operated to provide a braking force to the train), the communications system commands each remote unit to the same dynamic brake application.
The distributed power communications system also permits operation in an independent throttle control mode, where the operator segregates the train into a front group and a back group, and assigns remote units to each of the two groups. The assignments are dynamically controllable by the operator so that locomotives can be reassigned from the front group to the back group, and vice versa, while the train is operating.
The throttles of the remote units assigned to the front group follow the throttle positions of the lead locomotive. The throttles of the back group remote units are controlled independently of the throttles of the front group. This operational mode can be sued, for example, when the train is descending a mountain. As the train climbs the mountain, all remote units and the lead unit are providing maximum motive power (in a notch 8 throttle position). When the lead unit tops the crest, the lead locomotive throttle is moved to a dynamic brake position, while it is desired for the remote units to continue applying motive power to push the train over the mountain. As a mid-train remote tops the crest, it is reassigned to the front group so that dynamic brakes are applied at that remote unit. The process of reassigning the remote units from the back group to the front group continues until the last remote unit has been reassigned. In independent mode, the command message transmitted by the lead unit comprises a field for each remote unit of the train. Upon receipt at the remote unit, the pertinent field is checked and the remote unit is controlled according to the front or the back group.